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Nuclear Power

# Development of Al-Alloy Coating for Advanced Nuclear Systems Using Lead Alloys

[+] Author and Article Information
Yuji Kurata

Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan

Hitoshi Yokota, Tetsuya Suzuki

Ibaraki University, 4-12-1 Nakanarusawa,Hitachi 316-8511, Japan

J. Eng. Gas Turbines Power 134(6), 062902 (Apr 12, 2012) (7 pages) doi:10.1115/1.4005989 History: Received October 11, 2011; Revised October 14, 2011; Published April 09, 2012; Online April 12, 2012

## Abstract

Small and medium reactors using lead alloys as coolants are one of the promising reactor concepts with improved safety because of their thermal-physical and chemical properties. This paper focuses on the development of Al-alloy coating for nuclear systems using liquid lead-bismuth eutectic (LBE). Since corrosion attack becomes severe against structural steels at high temperatures in liquid LBE, it is necessary to improve the corrosion resistance of steels. An Al-alloy coating method using Al, Ti, and Fe powders, and laser beam heating has been developed. The main defects formed in the Al-powder-alloy coating process are surface defects and cracks. The conditions required to avoid these defects are the employment of the laser beam scanning rate of 20 mm/min and the adjustment of the Al concentration in the coating layer. According to the results of the corrosion tests at 550Â °C in liquid LBE, the Al-alloy coating layers on 316SS prevent severe corrosion attack such as grain boundary corrosion and LBE penetration observed in the 316SS without coating. The good corrosion resistance of the Al-alloy coating is based on the thin Al-oxide film, which can be regenerated in liquid LBE. From the viewpoint of the soundness of the produced Al-powder-alloy coating layers and the preservation of their corrosion resistance, it is estimated that the range of adequate Al concentration in the coating layer is from 4 to 12 wt. %.

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## Figures

Figure 1

Schematic illustration of Al-powder-alloy coating

Figure 2

Schematic diagram of static corrosion apparatus in liquid LBE

Figure 3

Oxygen concentration in liquid LBE during the corrosion test at 550 °C for 1000 h

Figure 4

Defects formed during Al-powder-alloy coating. (a) Sheet material (III), laser beam scanning rate: 60 mm/min, and (b) sheet material (V), laser beam scanning rate: 60 mm/min

Figure 5

Relationship between the Al concentration in the coating layer and that in the sheet material

Figure 6

Relationship between the number of cracks and the average Al concentration in the coating layer

Figure 7

SEM images of cross sections of specimens after the corrosion test in liquid LBE at 550 °C for 1000 h. (a) 316SS substrate without Al-alloy coating, (b) coated 316SS using sheet material (I), (c) coated 316SS using sheet material (II), and (d) coated 316SS using sheet material (VI). The scanning rate of 60 mm/min was employed for laser beam heating

Figure 8

Concentration profiles of Al, Ti, Cr, and Ni of Al-alloy coated 316SS after the corrosion test in liquid LBE at 550 °C for 1000 h [14]. Sheet material (II) was used for coating. The scanning rate of 60 mm/min was employed for laser beam heating

Figure 9

SEM image and results of point analyses for the corrosion film on the coating layer using sheet material (II) after the corrosion test in liquid LBE at 550 °C for 1000 h [14]

Figure 10

SEM images of cross sections of coated 316SS using sheet material (IV) after the corrosion test in liquid LBE at 550 °C for 1000 h. (a) Al-alloy coating without surface polishing, and (b) Al-alloy coating surface-polished before soaking in liquid LBE. The scanning rate of 20 mm/min was employed for laser beam heating

Figure 11

SEM images of cross sections of specimens after the corrosion test in liquid LBE at 550 °C for 3000 h. (a) Coated 316SS using sheet material (I), (b) and (c) coated 316SS using sheet material (II), and (d) coated 316SS using sheet material (VI). The scanning rate of 60 mm/min was employed for laser beam heating

Figure 12

Concentration profiles of Al, Ti, Cr, and Ni of Al-alloy coated 316SS after the corrosion test in liquid LBE at 550 °C for 3000 h. Sheet material (III) was used for coating. The scanning rate of 20 mm/min was employed for laser beam heating

Figure 13

Line analysis of the cross section of 316SS coated using sheet material (III) after the corrosion test in liquid LBE at 550 °C for 3000 h. The scanning rate of 20 mm/min was employed for laser beam heating.

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